The pharmacokinetic and pharmacodynamic characteristics of a long-acting growth hormone (GH) preparation (nutropin depot) in GH-deficient adults.

A pharmacokinetic-pharmacodynamic study of a long-acting GH [Nutropin Depot; somatropin (rDNA origin) for injectable suspension] was performed in 25 patients with adult GH deficiency. Single doses of 0.25 mg/kg and 0.5 mg/kg, based on ideal body weight, were administered sc. After either dose, serum GH concentrations rose rapidly in both sexes. In men, the lower dose maintained serum IGF-I levels within 1 SD of the mean for age and sex for 14-17 d; the higher dose raised IGF-I levels 2 SD above the mean. In most women, all of whom were receiving oral estrogen, the lower dose did not normalize IGF-I levels; the higher dose maintained IGF-I near the mean for approximately 14 d. Increases in IGF binding protein-3 and acid-labile subunit levels were observed in both sexes; however, a sex-related difference was not obvious. Fasting glucose and insulin concentrations were transiently elevated in men receiving the higher dose. Patients tolerated the injections well. We concluded that a single injection of Nutropin Depot at these doses in patients with adult GH deficiency increased serum IGF-I to within normal limits for 14-17 d. Estrogen-treated women required approximately twice the dose needed in men to produce comparable IGF-I concentrations.

Emi1 regulates the anaphase-promoting complex by a different mechanism than Mad2 proteins.

The anaphase-promoting complex/cyclosome (APC) ubiquitin ligase is activated by Cdc20 and Cdh1 and inhibited by Mad2 and the spindle assembly checkpoint complex, Mad2B, and the early mitotic inhibitor Emi1. Mad2 inhibits APC(Cdc20), whereas Mad2B preferentially inhibits APC(Cdh1). We have examined the mechanism of APC inhibition by Emi1 and find that unlike Mad2 proteins, Emi1 binds and inhibits both APC(Cdh1) and APC(Cdc20). Also unlike Mad2, Emi1 stabilizes cyclin A in the embryo and requires zinc for its APC inhibitory activity. We find that Emi1 binds the substrate-binding region of Cdc20 and prevents substrate binding to the APC, illustrating a novel mechanism of APC inhibition.

Emi1 is a mitotic regulator that interacts with Cdc20 and inhibits the anaphase promoting complex.

We have discovered an early mitotic inhibitor, Emi1, which regulates mitosis by inhibiting the anaphase promoting complex/cyclosome (APC). Emi1 is a conserved F box protein containing a zinc binding region essential for APC inhibition. Emi1 accumulates before mitosis and is ubiquitylated and destroyed in mitosis, independent of the APC. Emi1 immunodepletion from cycling Xenopus extracts strongly delays cyclin B accumulation and mitotic entry, whereas nondestructible Emi1 stabilizes APC substrates and causes a mitotic block. Emi1 binds the APC activator Cdc20, and Cdc20 can rescue an Emi1-induced block to cyclin B destruction. Our results suggest that Emi1 regulates progression through early mitosis by preventing premature APC activation, and may help explain the well-known delay between cyclin B/Cdc2 activation and cyclin B destruction.

The lore of the RINGs: substrate recognition and catalysis by ubiquitin ligases.

Recently, many new examples of E3 ubiquitin ligases or E3 enzymes have been found to regulate a host of cellular processes. These E3 enzymes direct the formation of multiubiquitin chains on specific protein substrates, and - typically - the subsequent destruction of those proteins. We discuss how the modular architecture of E3 enzymes connects one of two distinct classes of catalytic domains to a wide range of substrate-binding domains. In one catalytic class, a HECT domain transfers ubiquitin directly to substrate bound to a non-catalytic domain. Members of the other catalytic class, found in the SCF, VBC and APC complexes, use a RING finger domain to facilitate ubiquitylation. The separable substrate-recognition domains of E3 enzymes provides a flexible means of linking a conserved ubiquitylation function to potentially thousands of ubiquitylated substrates in eukaryotic cells.

Pharmacokinetics and pharmacodynamics of sibrafiban, an orally administered GP IIb/IIIa antagonist, following coadministration of aspirin and heparin.

Sibrafiban is a double prodrug that is converted to the inactive single prodrug and to the active GP IIb/IIIa antagonist after oral administration. This clinical investigation evaluated whether coadministration of oral aspirin or intravenous heparin would alter the pharmacokinetics or pharmacodynamics of oral sibrafiban. Twenty-four adult subjects received two of the following four combinations: sibrafiban alone, sibrafiban with ASA, sibrafiban with heparin, and sibrafiban with ASA and heparin, separated by a 2-week washout period. Concentration profiles of active drug in citrate and EDTA plasma were unchanged with coadministration of ASA or heparin. No pharmacodynamic interaction was seen with coadministration of heparin. Inhibition of platelet aggregation increased 4% to 55%, and Ivy bleeding time increased 58% to 87% with coadministration of sibrafiban and ASA. The combined pharmacodynamic effect of sibrafiban and ASA may indicate a potentially greater therapeutic effect but an increased risk of bleeding when these drugs are used in combination.

Treatment of allergic asthma with monoclonal anti-IgE antibody. rhuMAb-E25 Study Group.

BACKGROUND: Immune responses mediated by IgE are important in the pathogenesis of allergic asthma. A recombinant humanized monoclonal antibody (rhuMAb-E25) forms complexes with free IgE and blocks its interaction with mast cells and basophils. We studied the efficacy of rhuMab-E25 as a treatment for moderate-to-severe allergic asthma. METHODS: After a 4-week run-in period, we randomly assigned 317 subjects (age range, 11 to 50 years) who required inhaled or oral corticosteroids (or both) to receive either placebo or one of two regimens of rhuMAB-E25: high-dose rhuMAb-E25 (5.8 microg per kilogram of body weight per nanogram of IgE per milliliter or low-dose rhuMAb-E25 (2.5 microg per kilogram per nanogram of IgE per milliliter) intravenously on days 0 (half a dose), 4 (half a dose), and 7 (full dose) and then once every 2 weeks thereafter for 20 weeks. For the first 12 weeks of the study, the subjects continued the regimen of corticosteroids they had received before enrollment. During the following eight weeks, the doses of corticosteroids were tapered in an effort to discontinue this therapy. The primary outcome measure was an improvement in the asthma symptom score at 12 weeks, according to a 7-point scale, in which a score of 1 indicated no symptoms and a score of 7 the most severe symptoms. RESULTS: A total of 106 subjects were assigned to receive a high dose of rhuMAb-E25, 106 were assigned to receive a low dose, and 105 were assigned to receive placebo. At base line, the mean asthma symptom score was 4.0. After 12 weeks of therapy, the mean (+/-SE) scores were 2.8+/-0.1 in the high-dose group (P=0.008) and 2.8+/-0.1 in the low-dose group (P=0.005), as compared with 3.8+/-0.1 in the placebo group. At 20 weeks, the mean scores were 2.7+/-0.1 in both the high-dose group (P=0.048) and the low-dose group (P=0.14), as compared with 2.9+/-0.1 in the placebo group. More subjects in the two rhuMAb-E25 groups were able to decrease or discontinue their use of corticosteroids than in the placebo group, but only some of the differences were significant. After 20 weeks, serum free IgE concentrations decreased by a mean of more than 95 percent in both rhuMAb-E25 groups. The therapy was well tolerated. After 20 weeks, none of the subjects had antibodies against rhuMAb-E25. CONCLUSIONS: A recombinant humanized monoclonal antibody directed against IgE has potential as a treatment for subjects with moderate or severe allergic asthma.

Pharmacokinetics and pharmacodynamics of sibrafiban, an orally administered IIb/IIIa antagonist, in patients with acute coronary syndrome.

Sibrafiban is a double prodrug that is converted to the inactive single prodrug and to the active IIb/IIIa antagonist following oral administration. Pharmacokinetics (PK) and pharmacodynamics (PD) of oral sibrafiban and its metabolites were evaluated in patients postacute coronary syndrome receiving once- or twice-daily sibrafiban for up to 28 days at several dose levels. Mean peak concentrations of sibrafiban were < 5 ng/mL. Peak single prodrug concentrations occurred 1.7 +/- 1.0 (mean +/- SD) hours after sibrafiban dosing. Total apparent plasma clearance of the single prodrug was 40 +/- 15 L/h, and the elimination half-life was 2.3 +/- 0.8 hours. Mean values of the steady-state pharmacokinetics for total concentrations of the active drug over all doses were: time to peak plasma concentration, 5.0 +/- 1.7 hours; apparent clearance, 13.9 +/- 3.9 L/h; and half-life, 11.0 +/- 2.8 hours. Once-daily dosing resulted in high peak-trough excursions in active drug concentrations: trough concentrations were 21% +/- 6% of peak. Twice-daily dosing resulted in an AUC for the active drug on Day 28 that was 168% +/- 36% of that on Day 1, and steady-state trough concentrations were 54% +/- 10% of peak with sustained inhibition of platelet aggregation. Dose-adjusted steady-state active drug concentrations increased with increasing age and with decreasing renal function and body weight.

Platelet activation in patients after an acute coronary syndrome: results from the TIMI-12 trial. Thrombolysis in Myocardial Infarction.

UNLABELLED: This study was designed to determine the magnitude and time course of platelet activation during therapy of acute coronary syndromes with an oral platelet antagonist. BACKGROUND: Platelet activation and aggregation are central to the pathogenesis of the acute coronary syndromes (ACS). However, few data are available on levels of platelet activation over time in patients with ACS, especially in the setting of chronic glycoprotein (GP) IIb/IIIa inhibition. METHODS: The Thrombolysis in Myocardial Infarction (TIMI) 12 trial was a phase II, double-blind trial evaluating the effects of sibrafiban, an oral, selective antagonist of the platelet glycoprotein IIb/IIIa receptor in patients stabilized after an ACS. A subset of 90 of the 329 patients in the study had measurement of platelet activation as assessed by the expression of platelet associated P-Selectin on days 0, 7 and 28. Platelet activation was measured in blood samples that were fixed either immediately (spontaneous activation) or after 5 minute incubation with 0, 1 microM or 5 microM ADP in order to assess platelet responsiveness to very low or moderate stimulation. RESULTS: At baseline there was a significant elevation of spontaneous platelet activation as compared to samples obtained from normal donors or from patients who did not have acute coronary syndromes (ACS patients 27.6+/-18.7%, Normal controls 8.5+/-4.4%, Patient controls 10.9+/-7.1%, p < 0.005 for both). In addition, there was a significant decrease in the levels of platelet activation with time during the 28 days of treatment with sibrafiban. Nevertheless, even on day 28, the TIMI-12 patients continued to show elevated platelet activation in comparison to the control groups (p < 0.05 for both). CONCLUSIONS: These results suggest that platelets remain activated long after clinical stabilization post ACS. Although platelet activation decreased after one month of oral GPIIb/IIIa inhibition, levels remained higher than normal, suggesting the need for long-term antiplatelet therapy following ACS.